Photonic Integrated Circuits (PIC) have multiple relatively slow tuning degrees of freedom (DOF), that must be adjusted in order to stabilize the PICs to their optimum operating points. Methods are needed to perform this stabilization. Without such methods, large scale integration of many photonic devices on the PIC would not be possible.
One approach is to associate with each tuning DOF a probe point and actuate feedback on the DOF based on the probe observation, but this is cumbersome and does not work well when the tuning DOFs are coupled.